1 //===-- HexagonCFGOptimizer.cpp - CFG optimizations -----------------------===// 2 // The LLVM Compiler Infrastructure 3 // 4 // This file is distributed under the University of Illinois Open Source 5 // License. See LICENSE.TXT for details. 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "Hexagon.h" 10 #include "HexagonMachineFunctionInfo.h" 11 #include "HexagonSubtarget.h" 12 #include "HexagonTargetMachine.h" 13 #include "llvm/CodeGen/MachineDominators.h" 14 #include "llvm/CodeGen/MachineFunctionPass.h" 15 #include "llvm/CodeGen/MachineInstrBuilder.h" 16 #include "llvm/CodeGen/MachineLoopInfo.h" 17 #include "llvm/CodeGen/MachineRegisterInfo.h" 18 #include "llvm/CodeGen/Passes.h" 19 #include "llvm/Support/Compiler.h" 20 #include "llvm/Support/Debug.h" 21 #include "llvm/Support/MathExtras.h" 22 #include "llvm/Target/TargetInstrInfo.h" 23 #include "llvm/Target/TargetMachine.h" 24 #include "llvm/Target/TargetRegisterInfo.h" 25 26 using namespace llvm; 27 28 #define DEBUG_TYPE "hexagon_cfg" 29 30 namespace llvm { 31 FunctionPass *createHexagonCFGOptimizer(); 32 void initializeHexagonCFGOptimizerPass(PassRegistry&); 33 } 34 35 36 namespace { 37 38 class HexagonCFGOptimizer : public MachineFunctionPass { 39 40 private: 41 void InvertAndChangeJumpTarget(MachineInstr*, MachineBasicBlock*); 42 43 public: 44 static char ID; 45 HexagonCFGOptimizer() : MachineFunctionPass(ID) { 46 initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry()); 47 } 48 49 const char *getPassName() const override { 50 return "Hexagon CFG Optimizer"; 51 } 52 bool runOnMachineFunction(MachineFunction &Fn) override; 53 }; 54 55 56 char HexagonCFGOptimizer::ID = 0; 57 58 static bool IsConditionalBranch(int Opc) { 59 return (Opc == Hexagon::J2_jumpt) || (Opc == Hexagon::J2_jumpf) 60 || (Opc == Hexagon::J2_jumptnewpt) || (Opc == Hexagon::J2_jumpfnewpt); 61 } 62 63 64 static bool IsUnconditionalJump(int Opc) { 65 return (Opc == Hexagon::J2_jump); 66 } 67 68 69 void 70 HexagonCFGOptimizer::InvertAndChangeJumpTarget(MachineInstr* MI, 71 MachineBasicBlock* NewTarget) { 72 const TargetInstrInfo *TII = 73 MI->getParent()->getParent()->getSubtarget().getInstrInfo(); 74 int NewOpcode = 0; 75 switch(MI->getOpcode()) { 76 case Hexagon::J2_jumpt: 77 NewOpcode = Hexagon::J2_jumpf; 78 break; 79 80 case Hexagon::J2_jumpf: 81 NewOpcode = Hexagon::J2_jumpt; 82 break; 83 84 case Hexagon::J2_jumptnewpt: 85 NewOpcode = Hexagon::J2_jumpfnewpt; 86 break; 87 88 case Hexagon::J2_jumpfnewpt: 89 NewOpcode = Hexagon::J2_jumptnewpt; 90 break; 91 92 default: 93 llvm_unreachable("Cannot handle this case"); 94 } 95 96 MI->setDesc(TII->get(NewOpcode)); 97 MI->getOperand(1).setMBB(NewTarget); 98 } 99 100 101 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) { 102 // Loop over all of the basic blocks. 103 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end(); 104 MBBb != MBBe; ++MBBb) { 105 MachineBasicBlock *MBB = &*MBBb; 106 107 // Traverse the basic block. 108 MachineBasicBlock::iterator MII = MBB->getFirstTerminator(); 109 if (MII != MBB->end()) { 110 MachineInstr *MI = MII; 111 int Opc = MI->getOpcode(); 112 if (IsConditionalBranch(Opc)) { 113 114 // 115 // (Case 1) Transform the code if the following condition occurs: 116 // BB1: if (p0) jump BB3 117 // ...falls-through to BB2 ... 118 // BB2: jump BB4 119 // ...next block in layout is BB3... 120 // BB3: ... 121 // 122 // Transform this to: 123 // BB1: if (!p0) jump BB4 124 // Remove BB2 125 // BB3: ... 126 // 127 // (Case 2) A variation occurs when BB3 contains a JMP to BB4: 128 // BB1: if (p0) jump BB3 129 // ...falls-through to BB2 ... 130 // BB2: jump BB4 131 // ...other basic blocks ... 132 // BB4: 133 // ...not a fall-thru 134 // BB3: ... 135 // jump BB4 136 // 137 // Transform this to: 138 // BB1: if (!p0) jump BB4 139 // Remove BB2 140 // BB3: ... 141 // BB4: ... 142 // 143 unsigned NumSuccs = MBB->succ_size(); 144 MachineBasicBlock::succ_iterator SI = MBB->succ_begin(); 145 MachineBasicBlock* FirstSucc = *SI; 146 MachineBasicBlock* SecondSucc = *(++SI); 147 MachineBasicBlock* LayoutSucc = nullptr; 148 MachineBasicBlock* JumpAroundTarget = nullptr; 149 150 if (MBB->isLayoutSuccessor(FirstSucc)) { 151 LayoutSucc = FirstSucc; 152 JumpAroundTarget = SecondSucc; 153 } else if (MBB->isLayoutSuccessor(SecondSucc)) { 154 LayoutSucc = SecondSucc; 155 JumpAroundTarget = FirstSucc; 156 } else { 157 // Odd case...cannot handle. 158 } 159 160 // The target of the unconditional branch must be JumpAroundTarget. 161 // TODO: If not, we should not invert the unconditional branch. 162 MachineBasicBlock* CondBranchTarget = nullptr; 163 if ((MI->getOpcode() == Hexagon::J2_jumpt) || 164 (MI->getOpcode() == Hexagon::J2_jumpf)) { 165 CondBranchTarget = MI->getOperand(1).getMBB(); 166 } 167 168 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) { 169 continue; 170 } 171 172 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) { 173 174 // Ensure that BB2 has one instruction -- an unconditional jump. 175 if ((LayoutSucc->size() == 1) && 176 IsUnconditionalJump(LayoutSucc->front().getOpcode())) { 177 MachineBasicBlock* UncondTarget = 178 LayoutSucc->front().getOperand(0).getMBB(); 179 // Check if the layout successor of BB2 is BB3. 180 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget); 181 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) && 182 JumpAroundTarget->size() >= 1 && 183 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) && 184 JumpAroundTarget->pred_size() == 1 && 185 JumpAroundTarget->succ_size() == 1; 186 187 if (case1 || case2) { 188 InvertAndChangeJumpTarget(MI, UncondTarget); 189 MBB->replaceSuccessor(JumpAroundTarget, UncondTarget); 190 191 // Remove the unconditional branch in LayoutSucc. 192 LayoutSucc->erase(LayoutSucc->begin()); 193 LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget); 194 195 // This code performs the conversion for case 2, which moves 196 // the block to the fall-thru case (BB3 in the code above). 197 if (case2 && !case1) { 198 JumpAroundTarget->moveAfter(LayoutSucc); 199 // only move a block if it doesn't have a fall-thru. otherwise 200 // the CFG will be incorrect. 201 if (!UncondTarget->canFallThrough()) { 202 UncondTarget->moveAfter(JumpAroundTarget); 203 } 204 } 205 206 // 207 // Correct live-in information. Is used by post-RA scheduler 208 // The live-in to LayoutSucc is now all values live-in to 209 // JumpAroundTarget. 210 // 211 std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn( 212 LayoutSucc->livein_begin(), LayoutSucc->livein_end()); 213 std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn( 214 JumpAroundTarget->livein_begin(), 215 JumpAroundTarget->livein_end()); 216 for (const auto &OrigLI : OrigLiveIn) 217 LayoutSucc->removeLiveIn(OrigLI.PhysReg); 218 for (const auto &NewLI : NewLiveIn) 219 LayoutSucc->addLiveIn(NewLI); 220 } 221 } 222 } 223 } 224 } 225 } 226 return true; 227 } 228 } 229 230 231 //===----------------------------------------------------------------------===// 232 // Public Constructor Functions 233 //===----------------------------------------------------------------------===// 234 235 static void initializePassOnce(PassRegistry &Registry) { 236 PassInfo *PI = new PassInfo("Hexagon CFG Optimizer", "hexagon-cfg", 237 &HexagonCFGOptimizer::ID, nullptr, false, false); 238 Registry.registerPass(*PI, true); 239 } 240 241 void llvm::initializeHexagonCFGOptimizerPass(PassRegistry &Registry) { 242 CALL_ONCE_INITIALIZATION(initializePassOnce) 243 } 244 245 FunctionPass *llvm::createHexagonCFGOptimizer() { 246 return new HexagonCFGOptimizer(); 247 } 248
